In state-of-the-art supplemental inflatable restraint (SIR) systems, the decision to deploy an air bag is based on an estimate of the severity of a crash, as determined by an analysis of vehicle acceleration. Although a crash does result in large acceleration values, other sources of acceleration, especially rough road conditions, can also produce large acceleration values.
SIR algorithms use various boundaries or measures to determine if the air bag needs to be deployed. These boundaries and measures are set to only deploy on crash events, not rough road. Although a crash generally exhibits much larger vehicle acceleration than a rough road, there are some road conditions which generate accelerations close to crash conditions, and which, when multiplied by a factor of 2, as a standard immunity goal, cannot be reliably separated from high speed crashes using these boundaries and measures.